Conventionally, as a backlight unit incorporated into a liquid crystal display, there has been used a backlight unit comprising a lamp as a source for generating light rays, a light guiding plate disposed laterally of the lamp for guiding the light rays emitted from the lamp toward a front surface side, and a light diffusing sheet formed on a front surface side of the light guiding plate (on a screen side of the liquid crystal display).
As the light diffusing sheet, there has been proposed a light diffusing sheet comprising a light diffusing layer formed by applying a resinous composition including dispersed resinous beads on a surface of a base sheet made of synthetic resin such as polyethylene terephthalate (see Japanese Utility Model Publication No. Hei 5-73602) In this light diffusing sheet, the light rays transmitted through the light diffusing layer can be uniformly diffused by the resinous beads, resulting in enhanced luminance of the screen of the liquid crystal display.
To suppress partial adhesion (sticking) between a rear surface of the light diffusing sheet and a front surface of the light guiding plate and to thereby prevent a luminance nonuniformity of the screen, there has been proposed a light diffusing sheet comprising a sticking-proof layer formed by applying a resinous composition including dispersed resinous beads on a rear surface of a base sheet (for example, see Japanese Utility Model Publication No. Hei 7-8803).
By the way, these light diffusing sheets have a drawback in that these sheets are subject to deformation due to heat because the base sheets are made of the synthetic resin. On the other hand, the lamp as the source for generating light rays is adapted to emit light and generate heat simultaneously. In general, a portion of the light diffusing sheet in the vicinity of the lamp is exposed to temperatures of approximately 80 to 90° C. For this reason, the light diffusing sheet is thermally deformed and partially deflected. The deflection causes the luminance nonuniformity of the screen.